I was someone who defended The Last Jedi when it came out -- I still think it's a good film, but it's pretty clear that it has divided the fanbase. And to be honest, similar to The Force Awakens, it really doesn't hold up as well to me on repeat viewings, and I think I've discovered why (to me at least)
Poor character development.
This started with TFA - you advertised the original trio of Luke, Han, and Leia are returning and a passing of the torch so to speak to the new generation, and...you kill Han, have Han and Leia meet for 5 mins, have Leia and Luke never actually meet, have Han and Luke never actually meet, and now Han and Luke are dead, and Carrie Fisher is gone. That reunion can never happen.
Instead too much was crammed into TFA - if Rey, Finn, and Poe are the new 'Luke Han and Leia' -- then why have they never been together until the final moments of TLJ? The trilogy is 2/3 over and the main characters barely even know each other...and we barely even know them because the films have to bounce around to Hux, to Rose, to Snoke, etc.
The only character who has been well developed, imo, is Kylo Ren...and perhaps that is why he's well-received. It's hard for Rey to have a character arc when she's instantly good instead of the hero's journey of learning.
While I liked the open -endedness of TLJ's ending, really that could have just been a coincidence of executives having no clue where they are going with this franchise, which is frightening because you are pumping out films every year...with no overarching goal.
Solo was boring to me...and I've never been bored in a Star Wars movie before. It wasn't as bad as I thought it would be...it was just meh...so if the future films are just going to be pumped out like Solo has been, and the episodic films have not been developed, then perhaps Disney should slow it down...and regroup before they turn the greatest film franchise ever into the DCEU.